Poly(ethylene-co-vinyl acetate) (PEVAc) nanocomposites containing exfoliated α-zirconium phosphate (ZrP) have been prepared using a simple solution mixing method to improve their barrier and mechanical properties. ZrP was pre-exfoliated with a surfactant, followed by additional targeted surface functionalization and surfactant exchange to allow for hydrogen bonding of ZrP with the acetate functionality on PEVAc and to improve ZrP surface hydrophobicity. The solvent is found to play an important role in stabilizing ZrP exfoliation in the presence of PEVAc to retain full exfoliation and homogeneous dispersion upon the removal of the solvent. The PEVAc/ZrP nanocomposite exhibits greatly improved oxygen barrier, melt strength, and mechanical properties. The usefulness of the present study for the preparation of olefinic polymer nanocomposites is discussed.

Nanocomposites with exfoliated 2D materials are highly sought after due to resulting material enhancement of barrier and increased modulus among others. In the past, this was achieved by using polyols that were effective but caused a significant drop in the glass transition temperature of the nanocomposite. In this contribution, α-zirconium phosphate (ZrP) nanoplatelets were covalently modified to allow for dispersion in solvents with varying hydrophobicity and poly­(methyl methacrylate) (PMMA) for the first time. The nanoplatelets were prepared by using a polyetheramine surfactant to achieve exfoliation, followed by modification with epoxides. Combinations of different epoxides were shown capable of tuning the functionality and hydrophobicity of the exfoliated ZrP in organic media. After grafting glycidyl methacrylate and cyclohexene oxide to the surface of ZrP, an in situ free radical polymerization of MMA allowed for high concentrations of self-assembled exfoliated ZrP in a PMMA matrix.

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Dual-epoxide modification of α-zirconium phosphate (ZrP) nanoplatelets containing a bromine initiator was performed for surface-initiated activators regenerated by electron transfer atom transfer radical polymerization, resulting in poly(methyl methacrylate)-grafted ZrP (ZrP-g-PMMA) for dispersion in PMMA matrix. The morphology of the PMMA nanocomposites with variations in grafting density (σ) and grafted PMMA length (N g ) on ZrP-g-PMMA with a fixed PMMA matrix chain length (N m ) was investigated using transmission electron microscopy. Various types of polymer brush structures, including mushroom, semi-dilute polymer brush, and concentrated polymer brush structures, were prepared, which correspond to the wetting and dewetting phenomena of ZrP-g-PMMA in the PMMA matrices. The dual-epoxide functionalization helps decrease ZrP surface energy and improve the configurational entropy of grafted polymer chains, which results in the penetration of the matrix PMMA chains into the grafted brush layer at a low σ = 0.07 chain/nm 2 even when N g /N m < 0.36. The rheological study in the melt state reveals that the flow properties of the PMMA nanocomposites can be tuned via changing the loading of nanoplatelets or varying the grafting characteristics at the interface between ZrP and PMMA matrix. Furthermore, the rheological behavior of PMMA/ZrP-g-PMMA which contains two-dimensional (2D) nanoplatelets was found to be significantly different from that of the PMMA/silica-g-PMMA which contains spherical nanoparticles. This drastic discrepancy in their rheological behaviors is likely caused by the anisotropic nature of the 2D nanoplatelets in PMMA. The implication of the present study on the preparation of thermoplastic nanocomposites containing 2D nanoplatelets is discussed.

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